Late Quaternary Volcanic Stratigraphy Within a Portion of the Northeastern Tongariro Volcanic Centre
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Copyright is owned by the Author of the thesis. Permission is given for a copy to be downloaded by an individual for the purpose of research and private study only. The thesis may not be reproduced elsewhere without the permission of the Author. LATE QUATERNARY VOLCANIC STRATIGRAPHY WITHIN A PORTION OF THE NORTHEASTERN TONGARIRO VOLCANIC CENTRE A thesis presented as partial fulfilment of the requirements for the degree of Doctor of Philosophy in Soil Science By Shane Jason Cronin Massey University Palmerston North New Zealand 1996 Mount Ruapehu viewed from the east, July 1996. Fresh tephra covers snow on the northern sector of the volcano. ii ACKNOWLEDEGMENTS I thank Vince Neall, Bob Stewart and Alan Palmer for all their help during the course of this study. The enthusiasm and passion they have for their science has taught me that geology is not just a job, nor a discipline, but a lifelong process of discovery. In particular I thank Vince for "letting me loose" on this project, even if it seemed that I was heading in the wrong direction at times. Cleland Wallace, John Kirkman, Brent Alloway and David Lowe have all provided valuable and highly appreciated input into various parts of this work, as have journal reviewers listed within the thesis. I was the grateful benefactor of funding from the New Zealand Vice Chancellors Committee, the Helen E. Akers Scholarship fund (twice!), the Massey University Graduate Research Fund and the Tongariro Natural History Society. Travel funding from the Royal Society of New Zealand (Young Scientists' Fund), Massey University Research Fund, and the New Zealand Vice Chancellors Committee (Ciaude McCarthy Fellowship) enabled me to attend two international conferences, which has greatly enhanced my Ph.D. experience. I am grateful to Justlands, the Department of Conservation and the Rangipo Forest Trust for access into parts of the study area. I thank all my contemporaries in the Department of Soil Science for making it such a relaxed and "down to earth" place to work, particularly John (pH) Morrell and Shivaraj (Bucket) Gurung. Last but not least, I thank my fa mily and Iris for their patient support during this work. iii ABSTRACT Investigation of the Late Quaternary volcanic stratigraphy within the andesitic Tongariro Volcanic Centre has elucidated the history of construction of the northeastern Ruapehu and eastern Tongariro ring plains and provided a lahar record for the Tongariro catchment. Volcaniclastic ring-plain sequences were correlated and dated using rhyolitic and andesitic marker tephras. The identification of distal rhyolitic tephras in the area was improved by the application of discriminant function analysis (DFA) to their electron microprobe determined glass chemistry. The Okaia, Omataroa and Hauparu Tephras and the Rotoehu Ash were identified for the first time in this area, providing a chronology for pre- 22.6 ka ring-plain sequences not previously investigated. DFA of ferromagnesian mineral chemistry proved useful for discrimination of andesitic tephras, with titanomagnetite being the most useful phase. Development of an andesitic tephrostratigraphy in pre-22.6 ka sequences was aided by clustering analysis and DFA. Seven andesitic marker tephras were identified using a range of parameters to supplement the rhyolitic tephrostratigraphy. Using the tephrochronologic framework, 15 packages of lahar deposits were identified on the northeastern Ruapehu ring plain (from >64 to c. 5.2 ka) and six on the eastern Tongariro ring plain (from >22.6 to 11.9 ka). Lahar deposition on both ring plains was most voluminous and widespread during the last (Ohakean) and antepenultimate (Porewan) stadials of the last glacial (Otiran). Holocene lahars were restricted to a narrow sector of the northeastern Ruapehu ring plain. They appear to have been triggered mostly in response to large-scale tephra eruptions of Ruapehu and Tongariro, and mostly occurred along the path of the Mangatoetoenui Stream. Lahar deposits and surfaces beside the Tongariro River were mapped in eight lahar hazard zones, with lahar recurrence intervals ranging from 1 in >15 000 years to 1 in 35 years. The largest number and volume of lahars in this catchment occurred in the period from 14.7 to 10 ka. The greatest population risk identified in the Tongariro catchment is part of Turangi, built within a 1 in 1000 year lahar-hazard zone. Other property and infrastructure at greater risk include the State Highway 1 bridge across the Mangatoetoenui Stream and the Rangipo Dam and Power Station, within a 1 in 35 year hazard zone. The landscape of the northeastern Ruapehu and eastern Tongariro ring plains has developed in relation to late Quaternary climate changes in addition to volcanic activity. During the last and antepenultimate stadials of the last glacial, major ring-plain aggradation by lahars and streams occurred. This was probably in response to greater physical weathering and glacier action on the volcanic cones providing abundant sediment for lahars. During the warmer interstadials of the last glacial, soil development within andesitic ring plain material was greatest, particularly when the rate of soil accretion was low. iv TABLE OF CONTENTS PREFACE Frontispiece . ii Acknowledgements iii Abstract iv Table of contents r V s l CHtl�HAPH��JTER;: ONE:. .IN . TRODUC. .TION, . OBJECTIVES,. .OUTLI . NE. OF. STUDY. AREA. AND� PREVIOUS WORK - 1.1 Introduction . 1 1.2 Objectives of study 1 1.3 Methods . 1 - 1.4 Geography of the study area 2 -1.5 Climate, soils and land use 4 -1.6 Regional geologic setting 6 -1.7 Tongariro Volcanic Centre 10 1.8 Previous work in and around the study area 10 -1.9 Summary and conclusions from previous work 15 1.10 References . 18 CHAPTER 2: RHYOLITIC TEPHROCHRONOLOGY 2.1 Introduction . 21 2.2 Additional methodology and notes 22 .... 2.3 Methods of identifying late Quaternary rhyolitic tephras on the ring 22 plains of Ruapehu and Tongariro volcanoes, New Zealand 2.4 Keywords 2.5 Introduction 2.6 Setting 2.7 Methods 2.7.1 Sample preparation and analysis 2.7.2 Statistical methods - 2.7.3 Tephra classification methodology 2.8 Results 2.8.1 Ferromagnesian assemblages 2.8.2 Glass chemistry and similarity coefficients 10-22 ka tephras 22-65 ka tephras 2.8.3 Canonical discriminant function analyses of glass analyses 10-22 ka tephras discriminant model Classification of 10-22 ka unknown tephras 22-65 ka tephras discriminant model Classification of 22-65 ka unknown tephras V CHAPTER 3: ANDESITIC TEPHROCHRONOLOGY 3.1 Introduction . 41 3.1.1 Photographs of the Upper Waikato Stream sequence 41 3.2 Contributions of co-authors 44 3.3 Sourcing and identifying andesitic tephras using major oxide 45 titanomagnetite and hornblende chemistry, Egmont volcano and Tongariro Volcanic Centre, New Zealand 3.3.1 Introduction 45 3.3.2 Methods 48 3.3.3 Statistical methods 48 3.3.4 Discrimination between sources 49 Titanomagnetite 49 Hornblende 50 3.3.5 Discrimination of individual Egmont volcano-sourced tephras 52 Ti tanomagnetite 52 Hornblende 53 3.3.6 Summary and conclusions 55 3.3.7 Acknowledgements 56 3.4 A multiple-parameter approach to andesitic tephra correlation, 56 Ruapehu volcano, New Zealand - 3.4.1 Introduction 57 3.4.2 Setting 57 3.4.3 Methods 59 3.4.4 Statistical methods 59 3.4.5 Stratigraphy and distribution of 23-75 ka andesitic tephras 61 3.4.6 Physical properties and mineralogy of 23-75 ka andesitic tephras 63 3.4.7 Mineralogy 64 3.4.8 Mineral chemistry of 23-75 ka andesitic tephras 66 3.4.9 Titanomagnetite (discrimination of Marker Units 1, 2 and 6) 67 3.4.10 Hornblende (discrimination of Marker Unit 4) 71 3.4.11 Olivine (discrimination of Marker Unit 5) 73 - 3.4.12 Other phases 74 "' 3.4.13 Conclusions 75 3.4.14 Acknowledgements 76 3.5 Combined reference list . 77 CHAPTER 4: PALEOSOL DEVELOPMENT AND PALEOCLIMATIC INVESTIGATIONS OF THE RING PLAIN SEQUENCE 4.1 Introduction . 81 4.2 Investigation of an aggrading paleosol developed into andesitic ring 82 plain deposits, Ruapehu volcano, New Zealand. 4.3 Introduction 82 4.4 Setting 83 4.5 Stratigraphy 83 -4.6 Physical description 84 4.7 Mineralogy of ash grade material 86 4.8 M��s M 4.9 Results and discussion 88 4.9.1 Primary ash mineralogy 88 4.9.2 Siliceous phases 88 4.9.3 Secondary minerals 90 - 4.10 Relationship of Ruapehu ring-plain sequence to climate record for 94 southern North Island vi 4.11 Conclusions 96 4.12 Acknowledgements 97 4.13 References . 98 CHAPTER 5: THE LAHAR RECORD AND CONSTRUCTION OF THE NORTHEASTERN RUAPEHU AND EASTERN TONGARIRO RING PLAINS 5.1 Introduction .................................................. 101 5.2 A late Quaternary stratigraphic framework for the northeastern 102 Ruapehu and eastern Tongariro ring plains, New Zealand 5.3 Keywords 102 5.4 Introduction 102 5.5 Setting 103 5.6 Time control 103 5.7 Terminology and identification of ring plain deposits 103 5.8 Present channel geography 106 .9 Group 1 - Northeastern Ruapehu streams 107 5.10 Group 2 - Streams draining both volcanoes 110 �5.11 Group 3-Eastern and northeastern Tongariro streams 111 .12 Lahar distribution on the eastern ring-plain sectors from 23 ka to the present 113 - 5.13 Source and generation of lahars 118 , 5.14 Summary and conclusions 122 5.15 Acknowledgements 122 5.16 References .................................................. 123 CHAPTER 6: LAHAR HISTORY AND LAHAR HAZARD OF THE TONGARIRO RIVER 6.1 Introduction ................................................. 125 6.2 Lahar history and lahar hazard of the Tongariro River, northeastern 126 Tongariro Volcanic